Diseases and accidents leading to nervous system damage or degeneration are among the leading causes of mortality and morbidity in many countries. For example, approximately 700,000 people suffer a first or recurrent stroke annually in the United States, resulting in over 150,000 deaths. Although stroke represents the most common cause of damage to the central nervous system (CNS), a number of other conditions are also significant causes of functional deficits due to loss of brain tissue, either as a direct consequence of injury, or secondary to events such as swelling. Among these are primary brain tumors, brain metastases, and surgery for these or other conditions.
Strokes are a result of a sudden disruption of blood flow to a part of the brain and occur when a blood vessel that normally supplies brain tissue either bursts or becomes transiently or permanently blocked, such as by a blood clot (e.g., a thromboembolus) or other embolus or obstruction. The resulting disruption in normal blood flow deprives the affected tissue of needed oxygen and nutrients and can also impair removal of waste products, resulting in damage to, or death of, nervous system cells. Currently the only therapy for ischemic stroke approved by the U.S. Food and Drug Administration (FDA) is infusion of the thrombolytic agent tissue type plasminogen activator (tPA) within a short time window following the causative event. Such thrombolytic therapy was shown to be both safe and beneficial if delivered within 3 hours of the onset of symptoms (NINDS, Tissue plasminogen activator for acute ischemic stroke. The national institute of neurological disorders and stroke RT-PA stroke study group. N. Engl. J. Med. 333: 1581-1587, 1995).
While stroke is the third leading cause of death in industrialized countries, in most cases stroke is not fatal. However, stroke is a major cause of morbidity and a leading cause of serious, long-term disability. About 4.8 million stroke survivors are alive today in the United States, with a much larger total number worldwide. Many of these individuals suffer from functional limitations affecting the senses, motor activity, speech and/or the ability to understand speech, behavior, thought patterns, memory, emotions, or other aspects of cognition. Although functional deficits following stroke may be permanent, in many cases full or partial recovery is possible. The mainstays of treatment are supportive care and rehabilitation therapy, which frequently continues for months or years. Unfortunately, there are no pharmacological agents that have demonstrated efficacy in improving the long-term outcome of stroke.
Approximately 10,000-12,000 individuals suffer spinal cord injuries (SCI) each year in the United States, bringing the projected prevalence rate in the United States to nearly 280,000 by the year 2014 (DeVivo, M. J., 2002) Improvements in supportive care have greatly increased the survival rate following such injuries, but therapeutic options remain limited, and efforts focus on rehabilitation. Tumors affecting the spinal cord or meninges (either primary tumors or metastases) are also a significant source of morbidity.
Disorders of the nervous system also have a massive impact on society. Disorders of brain development, such as autism, now afflict about 1 in 166 children. The total number of individuals in the U.S. afflicted with autism, learning disabilities, and similar disorders is estimated to exceed 4 million. Neuropsychiatric disorders such as schizophrenia and bipolar disorders extract a huge cost in lifetime care for afflicted individuals as well as emotional toll on caregivers and families. Neurodevelopmental disorders such as autism are usually treated with behavioral therapies alone, and these strategies have limited success. Similarly, neuropsychiatric disorders such as schizophrenia and bipolar disorder have very limited therapeutic possibilities.
Thus there is a need in the art for improved treatments, particularly pharmacological treatments, that would enhance recovery following damage to the CNS and/or help improve CNS and cognitive function in neuropsychiatric and neurodevelopmental disorders. Common to a large range of CNS conditions is the concept that they centrally involve the function of synapses and their ability to change (i.e., plasticity). Thus, there is a need for new approaches to the identification of genes, molecules, cell types, and biological pathways that play a role in key nervous system properties such as plasticity and that can be modulated to provide a therapeutic benefit.